1. Field of the Invention
The present invention relates to a hydrogen sensor, and more particularly to a hydrogen sensor suited for measuring the concentration of hydrogen in a fuel gas, particularly a methanol-reformed gas, for use in a fuel
2. Description of Related Art
In response to concerns about global environmental pollution, in recent years extensive studies have been conducted on fuel cells for use as highly-efficient, clean power sources. Among such fuel cells, a polymer electrolyte fuel cell (PEFC) shows promise for various power sources including automobile use, by virtue of its advantages, such as operation at low temperature and high output density. A promising fuel gas for use in PEFC is a methanol-reformed gas or the like. In this connection, in order to enhance efficiency and like factors, a sensor capable of directly detecting hydrogen in a reformed gas is required.
Japanese Patent Publication (kokoku) No. 7-31153 proposes a sensor configured such that a working electrode, a counter electrode, and a reference electrode are disposed on an insulating base material while the three electrodes are unitarily covered with a gas permeable proton conductor membrane.
However, when the sensor disclosed in Japanese Patent Publication No. 7-31153 is used to measure the concentration of hydrogen in a methanol-reformed gas, unreacted methanol contained in the reformed gas influences the measurement of hydrogen concentration through the following mechanism: at a certain control electric potential set between the working electrode and the reference electrode (particularly when a high electric potential is set), methanol reacts with a resultant increase in current flowing between the working electrode and the counter electrode.